1. Field of the Invention
The present invention relates to an inkjet head and method for making the same. In particular, the present invention relates to an inkjet head including an actuator containing a piezoelectric material for converting electric energy into mechanical energy for ejecting ink and a manifold member constituting an ink channel for supplying ink for the actuator, wherein the actuator and the manifold member are jointed with an adhesive, and a method for making the same.
2. Description of Related Art
As for an inkjet head that ejects ink by using a shear mode of a piezoelectric material, such as PZT, for converting electric energy into mechanical energy for ejecting ink, a great feature is that ink liquid to be ejected has great latitude and nonaqueous inks such as oil inks and solvent inks can be ejected as compared to an inkjet head of the system using generation of air babble owing heating of ink as energy for ejecting.
However several solvent inks have corrodibility of expanding/transforming or solving a resinous member constituting an inkjet, or the like. Selection of an adhesive used for adhesive assembly of an ink channel part of an inkjet head is limited from the viewpoint of resistance to solvent inks.
According to the inventor's study of the resistance of an adhesive to various solvent inks, it is found that those having an enhanced crosslink density of an adhesive have a tendency to have an increased resistance to solvent inks, and simultaneously, it was found that a tendency for the adhesive to be stiff and have a higher Tg (glass transition point). As a result of this, all adhesives usable for solvent inks are those which have less flexibility and are solid.
The working temperature of an inkjet head is not limited to room temperature but the inkjet head is often used with heating, and it is necessary to obtain reliability for broad working temperature. An actuator that is a portion for head driving (ink jetting unit) is formed of ceramics material such as PZT and alumina, while a manifold member constituting an ink channel for supplying ink for this employs resin parts or metal parts from the viewpoint of suppressing increase of cost and easy processing. Therefore in assembling an inkjet head, there are some cases that parts having very different thermal expansion coefficients (linear expansion coefficients) must be jointed each other. At this time, a problem that distortion is generated between these members is caused by temperature change in working environment. Then there is a problem that a piezoelectric material of the actuator is affected by the stress owing such distortion, such that the characteristics are changed partially and variation in a driving voltage necessary for ink ejecting is found, which causes function failure owing to ejection speed abnormality.
Several ink-resistant adhesives require heating for being cured (for example, see JP-Tokukai-Hei-7-32597A). This increased temperature difference between a cure temperature of an adhesive in assembling an inkjet head and an environmental temperature in using the finished inkjet head, was a factor for compounding the problem of the above-described distortion generation, and narrows the range of selection of adhesives.
Further, even if there is no significant difference of a thermal expansion coefficient between an actuator and a manifold member, there are some of adhesives accompanied by volume shrinkage in being cured, and the volume shrinkage percentage increases in case of aiming at crosslink with a high density for improving ink-resistance. In case of a high stiffness of an adhesive and a large volume shrinkage percentage, there is a problem that distortion at the adhesive interface increases, consequently leading to function failure of the actuator as above, and additionally, interfacial peeling might be caused at worst.
As above, hitherto it has been difficult to satisfy both of securely performing the joint of an actuator containing a piezoelectric material and a manifold member and not damaging the characteristics of the piezoelectric material of the actuator.